JPH05160558A - Moisture resistant structure of module circuit - Google Patents

Abstract

PURPOSE:To provide the entitled moisture resistant structure of a module circuit capable of securing the moisture resistance almost without changing the electric circuit characteristics of strip line easy to form a high-frequency circuit. CONSTITUTION:Within the entitled moisture resistant structure of a module circuit, a strip line 2 of a module board 1 having a high-frequency circuit and a high-frequency device is to be covered with a water repellent porus film 3 in apparent (air bubble containing state) dielectric constant of not exceeding 2.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moistureproof structure for a module circuit, and more particularly to a moistureproof structure for a module circuit used at a high frequency of several GHz or more.

[0002]

2. Description of the Related Art Conventionally, a circuit used at a high frequency of several GHz or more is composed of a coaxial line or a triplate line,
Protected against wiring corrosion and electrical characteristic changes due to moisture and condensation. The stripline on the substrate is used by being enclosed in a ceramic container or provided with a moisture-proof coating.

[0003]

However, the coaxial line has a complicated connection, and the triplate line has a problem that the circuit formation is troublesome and the production cost is high.

On the other hand, the strip line solves the problems associated with wiring connection and circuit formation, but when a ceramic container is used, it has the drawbacks that the cost of the ceramic container is high and it is not suitable for mass production.

When a moisture-proof coating is used, since the dielectric constant of the moisture-proof coating material is considerably larger than that of air, electrical circuit characteristics fluctuate greatly. It is possible to design a circuit in consideration of this characteristic variation, but it is necessary to always coat the moisture-proof coating material as thick as the circuit design.
It is difficult to control the thickness of the film by ± several μm. In addition, when dew condensation is formed on the moisture-proof coating material of the strip line, the dielectric constant of water is as large as about 80, which greatly affects the electrical circuit characteristics, which is not preferable. In order to avoid the influence of dew condensation with the moisture-proof coating material, a thickness of 1 mm or more is required. In this case, however, the electrical circuit characteristics may change significantly only with the coating material, and the circuit design may not be able to absorb it.

It is an object of the present invention to provide a moisture-proof structure for a module circuit, which can secure moisture-proof property while hardly changing the electrical circuit characteristics of a stripline in which a high-frequency circuit can be easily formed.

[0007]

The moisture proof structure of the module circuit of the present invention is such that the strip line is covered with a water repellent porous film having an apparent dielectric constant of 2.0 or less. The apparent permittivity in the present invention is a permittivity in a state where bubbles such as air are contained in the pores of the porous film, not in the bulk.

[0008]

In the present invention, since the permittivity of the porous film covering the strip line is close to that of air, the electrical circuit characteristics are hardly affected. Further, since the porous film is water-repellent, the circuit can be protected from moisture and a module circuit excellent in high frequency characteristics and reliability can be constructed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings. FIG. 1 is a sectional view showing a moisture-proof structure of a module circuit according to an embodiment of the present invention. Reference numeral 1 is a module substrate having a back surface provided with a conductor layer, 2 is a strip line, and 3 is a water-repellent porous film having an apparent dielectric constant of 2.0 or less.

The porous film 3 can be formed on the strip line 2 with a silicone or fluorine coating material if necessary.

Specific examples of the water repellent porous film having an apparent dielectric constant of 2.0 or less include polytetrafluoroethylene (PTFE) and polyethylene (P
E), polypropylene (PP), polystyrene (PS)
And porous films such as isomers of these and copolymers of these monomers.

If the apparent dielectric constant (dielectric constant of a film containing bubbles) of these porous films exceeds 2.0, electrical circuit characteristics are affected, so 2.0 The following is necessary, and preferably 1.5 or less. To achieve this dielectric constant, a porosity of 5 to 90% is required, depending on the dielectric constant of the initial film.

The thickness of these porous films is 0.1 m.
m or more is required, preferably 0.5 mm to 2.0 mm
The range is. If it is less than 0.1 mm, it may not be possible to remove the influence of condensed water. Even if the thickness exceeds 2.0 mm, the circuit characteristics are hardly affected, but it is desirable that the thickness does not exceed 2.0 mm for high-density mounting.

Next, the moisture-proof structure of the present invention will be described more specifically based on examples, but the present invention is not limited thereto.

Example 1. As a porous film, thickness 1
GORE-TEX film with a dielectric constant of 1.2 and 1.6 (porous PTFE: Japan GORE-TEX Co., Ltd.)
Band Rejection Filter Band Reject Filter formed on an alumina ceramic substrate.
It was placed on the ion filter (BRF) circuit and lightly pressed to cover the BRF circuit with air bubbles. The BRF circuit used was a microstrip line formed on an alumina ceramic substrate.

For comparison, instead of the porous film, a silicone potting material (JCR6143: manufactured by Toray Dow Corning Silicone) was used at 30 μm and 1
mm coating and curing at 150 ° C. for 2 hours to prepare a test piece.

Next, using each of the obtained test pieces, the electrical characteristics of the porous film and the presence or absence of water drops on the silicone potting material were evaluated at a measurement frequency of about 10 GHz. The results are shown in Table 1.

[0018]

[Table 1]

The sample of Example 1 showed almost the same loss as the initial loss of the BRF circuit, and showed almost no effect when water droplets dripped, and showed excellent moisture resistance. The test piece coated with 1 mm of silicone potting material had a BRF circuit loss of 3 dB, which was larger than the initial value, and the effect of dropping water droplets was not examined.

Example 2. The thickness of the GORE-TEX film (same as above) with a dielectric constant of 1.2 was changed to 0.5, 1.0 and 2.0 mm, and the silicone potting material (JC
It was adhered on the BRF circuit via R6143). JCR
The thickness of 6143 was set to about 10 μm and cured at 150 ° C. for 2 hours.

Next, the same evaluation as in Example 1 was carried out using each of the obtained test pieces. The results are shown in Table 2.

[0022]

[Table 2]

Similar to the above embodiment, it is almost the same as the initial loss of the BRF circuit, and even when water droplets are dripped on the porous film, the influence is hardly seen. Also, Reject
When the deviation of the ion frequency was also evaluated, the same result was obtained.

Example 3. On an alumina ceramic substrate,
Using an evaluation substrate provided with a chrome / gold thin-film counter wiring, the thickness of a GORE-TEX film (same as above) having an apparent dielectric constant of 1.2 was changed to 0.5, 1.0 and 2.0 mm, It adhered via a silicone potting material (JCR6143). The thickness of JCR6143 was about 10 μm and cured at 150 ° C. for 2 hours.

Next, using each of the obtained test pieces and an alumina ceramic substrate provided with a chromium / gold thin film facing wiring,
Moisture resistance was evaluated. The condition is PCT (Press
ure Cooker Test) 121 ° C., 2 atmospheres, a DC bias of 5 V was applied, and the change in insulation resistance due to migration of wiring was examined. The results are shown in Table 3.

[0026]

[Table 3]

An alumina ceramic substrate provided with a chromium / gold opposing wiring has an insulation resistance between wirings of 10 ⁶ Ω in about 10 minutes.
In contrast, in the test piece in which the porous film was bonded to the wiring via JCR6143, the insulation resistance did not decrease until 200 hours.

[0028]

The moisture-proof structure of the module circuit of the present invention has a structure in which a water-repellent porous film having an apparent dielectric constant of 2.0 or less is provided on a high-frequency circuit, so that the electrical circuit characteristics can be improved. It has excellent moisture resistance with almost no loss and can be suitably used for a circuit such as a high frequency module.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram showing a first embodiment of the present invention.

[Explanation of symbols]

 1 Module substrate 2 Stripline 3 Porous film

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takei Fujiwara, 8-1, 1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Communication Equipment Works (72) Inventor Hiroyuki Sato 8-1-1, Tsukaguchihonmachi, Amagasaki No. Mitsubishi Electric Corporation Communication Equipment Works (72) Inventor Fumiaki Baba 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation

Claims (1)

[Claims] 1. A moisture-proof structure for a module circuit, wherein a strip line of a module substrate having a high-frequency circuit and a high-frequency device is covered with a water-repellent porous film having an apparent dielectric constant of 2.0 or less.